Since 1988 the Advanced Electromagnetic Protection Group at the National Research Council of Canada has been involved in the development of an Expert System capable of alleviating the complexity of the electromagnetic hardening process, a process that is designed to lower the susceptibility of an electrical system to electromagnetic emission. A first version of the Expert System is called HardSys and is described by Lo Vetri, J., Abu-Hakima, S., Podgorski, A. S., and Costache, G., entitled "HardSys: Applying Expert System Techniques to Electromagnetic Hardening", published May 23-25, 1989 in IEEE 1989 National Symposium on Electromagnetic Compatibility, pp. 383-385, Denver, Co., and was based on an object-oriented knowledge representation.
The concept of the first version of HardSys was based on a minimum spanning tree algorithm taught by E. W. Dijkstra in a publication entitled "A Note on Two Problems in Connexion with Graphs", Numerische, Vol. 1, pp. 269-271, 1959 that allowed calculation of the worst case shielding path for a specified frequency range. Once the worst case shielding path was established and the discrete propagated ambient fields from all nodes were added in parallel, a total propagated ambient field obtained was verified with the total susceptibility of a receiving node, permitting determination of the likelihood of failure. The likelihood of failure was assigned six discrete, linguistic values for each frequency range. It was concluded during the system validation process that in the discrete system definition, even if the ambient field and system susceptibilities discrete scales were divided into more sub-levels, it would be impossible to drastically improve the accuracy of the Expert System or to expand the dynamic range of the likelihood of failures.
A second version of HardSys described by Kass, S. B., entitled "Proposed Enhancements to the HardSys Electromagnetic Hardening Advisor", Internal Report, National Research Council of Canada, Advanced Electromagnetic Protection Group, Ottawa, Canada, Mar. 12, 1991, was based on work intended to overcome the difficulties associated with the implementation of the fixed discrete ambient field and the use of discrete system susceptibility scales and a failure likelihood. The second version of HardSys showed that the implementation of a trapezoidal representation for fuzzy quantities taught by Dubois, D., and Prade, H., in a publication entitled "Possibility Theory, An approach to Computerized Processing of Uncertainty", Plenum Press, New York & London, 1988, assures greater freedom when specifying system attributes and the analysis in terms of fuzzy quantities gives the user a more complete picture of the effects of interaction than that which was based on a fixed linguistic level (good, bad, very good, very bad) for a specified frequency range. A trapezoidal representation of fuzzy quantities improved the accuracy of the analysis for high likelihood of failure; however, it did not allow extension of the dynamic range of the analysis to account for the low likelihood of failure.